1. Field of the Invention
The present invention relates to a method for adjusting the wheel alignment of a vehicle, and particularly to a method for adjusting a wheel angle of a vehicle in which a wheel of a vehicle with a tire fitted thereto is rotated on a wheel rotating surface, the tire is deformed, and the forces thereby generated are measured. The wheel angle is then adjusted on the basis of the results of the measurement providing an improvement in the running stability of the vehicle and a reduction in the wear of only one side of the tire.
2. Description of the Related Art
In general, wheels are provided with a camber angle which ensures the running stability of the vehicle and are also provided with a toe angle for preventing wear on only one side of the tire caused by the camber angle. In the present specification, the term "one-sided wear" is used hereafter to describe a state where, upon observation of the state of wear of a worn tire, it can be seen that the amount of wear extending from one tread shoulder portion to the other tread shoulder portion changes in a tapered fashion, i.e. a state where one tread shoulder portion is more worn than the central portion of the tread and the other tread shoulder portion.
Conversely, the wheel may be provided with a toe angle for balancing the forces generated at the front tires and at the rear tires thereby ensuring the running stability of the vehicle and may be provided with a camber angle to prevent one-sided wear caused by the toe angle. Alternatively, the toe angle and camber angle may both be adjusted in combination to optimize the running stability of the vehicle and minimize the one-sided wear of the tire under the restraints imposed by the vehicle such as the structural dimensions thereof and the like.
Accordingly, in order to improve the running stability of the vehicle and resistance of the tire to one-sided wear during driving, it is necessary to adjust the toe angle and camber angle, which are the wheel angles (positional angles) provided to each wheel. In the conventional method of adjusting the toe and camber angle, generally, the angle and dimensions of each wheel are measured and the measured toe and camber angles are then adjusted so as to match the target values set when the vehicle was designed.
However, while tires have various characteristics such as ply steer, which is caused by the internal construction of the tire; toe force, which is generated because the tire is at an angle to the direction in which the vehicle is advancing caused by the fact that the direction in which the wheel is rotating is different to the direction in which the vehicle is advancing; self-aligning torque, which is generated because the direction of advancement does not match the point on the road-contacting surface to which the force is applied; camber thrust, which is generated when the tire deforms due to the camber angle of the wheel depending on the rigidity of the tire governed by the internal structure of the tire; camber moment, which is generated by the difference between the left and right sides of the road-contacting surface; conicity, which arises from manufacturing errors inherent in industrial products; and rolling resistance, which differs depending on the internal structure and the material used such as the rubber, these characteristics depend on and vary in accordance with the load applied to the wheel. Further, these characteristics also depend on the type of tire.
In other words, the afore-mentioned forces are generated by the deformation of the tire. The force generated by the tire to control its running direction while causing the vehicle to advance is the sum of the afore-mentioned forces. Therefore, regardless of the type of tire, this force differs depending on the load distribution of the vehicle to which the tire is fitted and the alignment of the wheel. Accordingly, to meet the demands for increased vehicle speed and better directional stability, a wheel alignment adjustment method is necessary which provides better running stability and one-sided wear resistance.
The technology disclosed in Japanese Patent Application Publication (JP-B) No. 51-18681 is known as a conventional adjustment method focussing on the characteristics of the tire. The wheel is driven using a plurality of rollers and each of the forces generated by the rollers is measured. The toe angle and camber angle are then measured on the basis of the direction and magnitude of the measured force. However, it has been verified that the force generated by the contact between the tire and the road differs depending on the configuration of the contact between the tire and the road surface. Because of this, the configuration of the contact between the tire and a roller are is very different from the configuration of the contact between the tire and the actual road surface. Therefore, the characteristics of the force generated differ greatly between the road surface and the roller.
More specifically, although the force generated using the roller resembles the lateral force caused by the ply steer and the provision of the toe angle when running on an actual road surface, the alignment and the size of the force are greatly different from those occurring when the wheel is run on an actual road surface. Moreover, any camber thrust is barely detectable. In addition, the forces generated in the tire arising from the deformation of the tire caused by external disturbances from the numberless bumps in the road surface cannot be detected.
Accordingly, In the above-described conventional art, the measured force exhibits values which are different from values obtained from an actual road surface. In order to correct the measured values to the values obtained from an actual road surface, data expressing the characteristics of the respective tires on an actual road surface is needed. Therefore the above-described conventional method lacks wide applicability in actual practice. Further, no technical information has been disclosed with regard to what angle the alignment should be adjusted to in order achieve the optimum alignment.
A technique is known in which a wheel is driven using a plurality of rollers which aims to achieve high running stability by bringing lateral forces to substantially zero (see Japanese Patent Application Laid-Open (JP-A) No. 7-5076). In this technique, a wheel which has a camber angle is given an alignment which generates a force in the opposite direction to the direction of the camber thrust in order to bring the generated lateral forces to zero.
However, even in this technique, in the same way as the previously described case, because the contact surface of the tire with the rollers is different from the contact surface of the tire with the actual road surface, any camber thrust is almost undetectable. Moreover, in order to offset the force generated by the rotation of the wheel so as to bring the lateral force to zero, it is necessary to apply the force from the road surface generated by the running of the vehicle in the opposite direction to the direction of the force generated by the vehicle. In this case, the deformation of the road-contacting surface of the tire becomes even greater than when the tire is in a stationary state, and this deformation of the road-contacting surface is a factor in the generation of one-sided wear of the tire.
A method has been proposed (see JP-A 8-334440) for adjusting the alignment of a wheel by rotating the wheel on a substantially planar surface using a belt or the like, detecting the force generated by the wheel and adjusting the alignment on the basis of that force. However, an actual road surface is formed with innumerable bumps and hollows (protrusions and recesses) and a tire on a running vehicle is always deformed by these innumerable bumps and hollows. The load applied to each wheel also varies when the vehicle is running over bumps and hollows of a comparatively long cycle also deforming each tire so that the tire on a running vehicle is rotating while being affected by the force generated by the contact of the tire with the road surface and the force from the above deformations. In contrast, the force which can be detected by rotating the tire on a planar surface formed from a belt or the like is only the force which is generated by the contact of the tire with the belt surface. There is additionally none of the load variation which is generated by an actual road surface with the result that only a portion of the forces generated by running on an actual road surface can be detected using the conventional method. Accordingly, even if the alignment of a wheel is adjusted on the basis of the forces detected in conditions which are unaffected by load variation such as those generated by a substantially planar surface, the running stability will be improved for a vehicle running on an extremely level surface, however, there will be no improvement in other running characteristics and in one-sided wear.
More specifically, when a tire is running on an actual road surface, forces are generated by different generating mechanisms. In spite of the fact that these forces differ depending on the characteristics of the tire, the following conventional methods have been used: (1) a vehicle is actually run using specific tires, the angle at which one-sided wear is the least without losing running stability is found empirically, and the wheel is adjusted to this angle; (2) the wheel is adjusted to angle where the force measured on a planar surface is offset to the minimum possible (substantially zero); (3) the wheel is adjusted to an angle where only the specific force measured by running the wheel on a planar surface or on rollers is the minimum possible (substantially zero); (4) the wheel is adjusted to an angle obtained through some other object thereof is to provide a vehicle wheel alignment adjustment method which is unaffected by the suspension geometry of the vehicle, in which an angle of a wheel can be adjusted easily to an angle of the wheel which accords with the characteristics of the tire and which is able to ensure running stability suited for an actual road surface and also reduce one-sided wear.
When a tire is rotated by contact with an uneven road surface (a road surface having protrusions and recesses), the tire is deformed by load variations generated as the tire moves vertically relative to the ground-contacting surface of the tire and the lateral forces (specifically, the lateral force known as ply steer caused by the structure of the tire, the lateral force known as conicity caused by the manufacturing process, the lateral force due to the imparting of a slip angle (toe angle) to the wheel, and the lateral force known as camber thrust due to the imparting of a camber angle to the wheel) generated on the tire, by the deformation, all vary. In the technology disclosed in JP-A No. 10-7013, as was explained above, the angle of the wheel is adjusted on the basis of the variation in the lateral force generated in the tire when the deformation of the tire is at maximum or substantially maximum as the wheel travels over a step simulating an actual road surface (the variation in the load is occurred at the passage of the wheel over this step).
However, because the lateral force generated in the tire varies because of the deformation of the tire as the load changes or as the tire passes over a step, as was explained above, then as the factors causing these deformations in the tire disappear, the tire, which had been in a deformed state, attempts to method. However, none of these methods can be applied to a variety of different vehicles running on a variety of different tires.
Moreover, the present inventors measured the lateral force and longitudinal force generated in a tire when the vehicle wheel travels over a step and proposed a method for adjusting the wheel angle of a vehicle in such a way that variation in the lateral force at the time the longitudinal force is at a maximum or substantially maximum value was at a minimum (see JP-A No. 10-7013). In this method, the longitudinal force is measured to detect the timing at which the deformation of the tire is at maximum and the period in which the longitudinal force is at maximum or substantially maximum is taken as the period in which the amount of tire deformation is at maximum or substantially maximum.
However, the timing at which the longitudinal force changes depends on the suspension geometry of the vehicle. The suspension geometry of the vehicle sometimes causes the timing at which the tire deformation is at maximum or substantially maximum to fail to match up with the timing at which the longitudinal force of the vehicle is at maximum or substantially maximum. Accordingly, the accuracy of the above-described adjustment method is affected by the suspension geometry of the vehicle and it is not always possible to adjust the alignment of the wheel to the optimum even if the above-described method is used.